Magnetic resonance imaging (MRI) systems are frequently employed to provide guidance to interventionalists who are performing interventional procedures to diagnose or treat tissue in a patient. During interventional procedures, an interventional device (e.g., catheter) may be guided by an interventionalist (e.g., surgeon, radiologist) to a target tissue (e.g., tumor) or target area (e.g., heart) in a patient. Interventional devices may include, for example, needles, catheters, ablation devices, imaging devices, therapeutic devices, diagnostic devices, or other devices. These interventional devices are intracorporeal devices that may be maneuvered inside a patient's body. In an image guided interventional device insertion, the location of the device relative to the surrounding anatomy and target area are determined using the MRI system.
To assist in MRI image guided interventional procedures, techniques have been developed that track the location of an interventional device during the procedure. These techniques may update scan planes used by the MRI system so that the scan planes automatically track the device. Conventional methods and apparatus localize multiple markers with fixed positions on the apparatus. For example, optical tracking employs multiple cameras with different positions and orientations to measure the locations of optical markers. The optical markers may be reflective and the optical tracking apparatus may be self-contained and wireless. However, optical tracking is less than optimal for at least the reason that the optical markers must remain visible to the cameras throughout the entire procedure. By being forced to remain visible to the cameras, optical tracking limits the freedom of the interventionalist to freely wield the interventional device inside the magnet bore.
Other conventional techniques employ tuned coils containing fiducial markers. For example, passive fiducial marker tracking uses the signal enhancement produced by individual tuned coils that couple directly to a local fiducial marker. The fiducial markers are localized using specific sequence parameters to enhance the signal of the passive fiducial marker, while only slightly perturbing surrounding signal sources. While passive fiducial marker tracking allows an apparatus to be wielded more freely in the bore of the magnet of an MRI system without regard to camera visibility, the enhanced marker visibility and localization is highly dependent on a number of parameters. These parameters, which include the marker position and orientation, limit the ability of the interventionalist to freely wield the interventional device in the bore. In contrast, active fiducial marker tracking directly connects tuned coils containing fiducial markers to the magnetic resonance (MR) scanner. Active fiducial marker tracking treats the tuned coils as standard coils, which allows for easy integration with the MR system. Additionally, the apparatus can be localized regardless of marker orientation and position as long as the marker remains within the bore's imaging region. However, the markers must be connected to the MR system, which in conventional systems is achieved by coaxial cables. Unfortunately, the coaxial cables may hinder the interventionalist's ability to freely wield the device. Furthermore, coaxial cables snaking about the core may present safety issues for the patient.
While passive fiducial marker tracking and active fiducial marker tracking offer some improvements over optical tracking, both active and passive fiducial marker tracking have their own limitations. In some circumstances these techniques, which fix the scan plane relative to the interventional device, produce unsatisfactory results. For example, flexing of a catheter or needle on an interventional device may cause misregistration of the scan plane to the tissue in treatment. In other instances, the interventionalist performing the procedure may wish to view an image that does not correspond to a scan plane in the fixed relationship to the interventional device. When a different scan plan is desired, a time consuming manual adjustment of the scan plane is performed. In some clinical situations, when a patient is confined in an MRI apparatus during a procedure (e.g., heart ablation), it may be desirable to reduce time spent making adjustments.